Various types of fluids are used in operations related to the development and completion of wells that penetrate subterranean formations, and to the production of gaseous and liquid hydrocarbons from natural reservoirs in such wells. These operations include perforating subterranean formations, fracturing subterranean formations, modifying the permeability of subterranean formations, or controlling the production of sand or water from subterranean formations. The fluids employed in these oilfield operations may include drilling fluids, completion fluids, work-over fluids, packer fluids, fracturing fluids, stimulation fluids, conformance or permeability control fluids, consolidation fluids, and the like.
Hydraulic fracturing is one stimulation technique that is routinely performed on oil and gas wells to increase fluid production from subterranean reservoirs. Specially engineered fluids are pumped at high pressures and rates into the reservoir to be treated, causing fractures in the formation matrix to open. Proppants, such as ceramic beads or grains of sand, are carried within the fracturing fluid to keep the fracture open once the treatment is completed.
Matrix acidizing and acid fracturing are also techniques commonly used in order to stimulate the production or injectivity from wells that either produce hydrocarbons or are used for water injection. Acidizing of carbonate formations is typically carried out using hydrochloric, formic, or acetic acid in dilute aqueous solution with a number of other additives, such as those for corrosion inhibition, wettability alteration, etc. In sandstone formations, acidizing is usually carried out using solutions of hydrofluoric acid mixed typically with hydrochloric, acetic, formic, or a number of other organic acids. The chemistry of these fluids is more challenging because the sandstone formations being treated call for more aggressive solutions, due to the damage from aluminosilicate clays and drilling damage, and less-damaging fluids. This makes treating sandstone formations more difficult due to the complicated mineralogies and challenging temperatures.
One of the primary challenges in development of acidizing fluids for both carbonate and sandstone is the achievement of homogeneous placement of acid across formations with high permeability-heterogeneity across the productive interval. A number of techniques have been used to achieve improved acid diversion, including mechanical techniques, such as those employing packers and frac baffles, internal diverters that include chemicals that invade the porous rock matrix and generate temporary damage, and external particulate diverters. External particle-diverters have included rock salt, oil-soluble resins, and a number of other solids that degrade into water or oil-soluble materials.
Degradable polymers, such as those described in U.S. Pat. No. 7,166,560, have found use recently for acid-fracturing of carbonate formations, which hydrolyze to form soluble acids when exposed to temperatures typically encountered downhole. However, other degradable polymers are highly-sought after for matrix acid diversion, fluid-loss control in hydraulic fracturing and acid-fracturing applications, in addition to a wide variety of other applications that could benefit from degradable solids.
Scale deposition is a persistent problem that occurs in producing wells. Protecting wells from scale deposition is commonly accomplished by “squeezing” scale inhibitors into the formation matrix. This process is usually conducted as a separate step or treatment from stimulation or other treatments of the formation that typically requires the well to be shut in for a period of time. Reducing the number of scale treatments required to maintain productivity is therefore important.
Accordingly, a need exists for new treatment methods and fluids for treating subterranean formations in oil and gas wells that can combine in non-scale-inhibitor treatments a means for inhibiting or removing scale without requiring a separate scale inhibitor treatment.